Saying NBA players want “to be and be perceived as playing in a drug-free sport,” commissioner David Stern hopes to have a test for human growth hormone in place by the fall. “We expect that to happen, we really do, before the start of next season,” Stern said here Saturday night. Stern defended the league’s testing for performance-enhancing drugs in the wake of Hedo Turkoglu’s positive test and a 20-game ban announced this week. “Our players have been front and centre with us on this one,” he said. “We have six unannounced tests a year. Two of those are authorized out of season. And we have an independent group of experts that adds drugs to the list of prescribed drugs. And we test in a way that the samples get sent to an approved lab and we’re there.” Stern said once a blood-testing protocol is available for HGH it could lead to a “biological passport” that will follow players throughout their careers. “I think the blood test is the precursor to the biological passport,” he said. “And that’s a subject for discussion with the players’ association.”